The use of non-azeotropic fluid mixtures in a compression thermodynamic cycle, and for example in a heat pump, in order to improve the performance coefficient of said heat pump, has been the object of prior French patent application Nos. 2 337 855, 2 474 151, 2 474 666 and 2 497 931 corresponding to U.S. Pat. Nos. 4,089,186; 4,344,292; 4,350,020 and 4,406,135.
In particular, the published French patent application No. 2 474 151 discloses non-azeotropic mixtures having two constituents providing for an increase of the performances of a heat pump and hence a reduced operating cost thereof. The disclosed 2-constituent mixtures, however, do not provide for an increase of the thermal power for a given compressor.
The present invention has for object to provide specific fluids whereby the supplied thermal power and/or the performance coefficient of a heat pump may be increased. By using the fluid mixtures proposed according to the invention in a heat pump, it is thus possible to reduce the investment cost and the operation cost. As a matter of fact, the use of mixed working fluids according to the invention make possible an increase of the thermal capacity of a given heat pump, without modifying the components thereof, particularly without modification of the compressor. These fluid mixtures also provide for an increase of the performance coefficient.
Two conventional means can be used to increase the thermal power supplied by a heat pump. A first one is to equip said pump with a compressor of larger capacity, so as to suck in a larger input volume, but at the cost of an overinvestment. The other means for increasing the thermal capacity of the heat pump consists of using a working fluid whose boiling point is lower than that of the usual fluid. Such a substitution always results in a degradation of the performance coefficient and also in a more restrictive range of use of the machine, in view of the generally lower critical temperature of the fluid of lower boiling point.